Method for selecting of sidelink grant for a d2d ue in a d2d communication system and device therefor

ABSTRACT

A method for transmitting sidelink data by a User Equipment (UE) in a wireless communication system includes determining whether resource pool information for selecting a sidelink grant is configured by a base station; determining whether more sidelink data is available in a Sidelink Traffic Channel (STCH) than can be transmitted in a current Sidelink Control (SC) period; selecting resources for the sidelink grant from the resource pool information based on the resource pool information for selecting the sidelink grant being configured by the base station, and more sidelink data being available in the STCH than can be transmitted in the current SC period; selecting resources for the sidelink data based on the resources for the sidelink grant; and transmitting the sidelink data to another UE through the resources for the sidelink data. Further, the sidelink grant is for a next SC period after the current SC period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 16/267,716 filed on Feb. 5, 2019, which is a Continuation ofU.S. patent application Ser. No. 15/003,222 filed on Jan. 21, 2016 (nowU.S. Pat. No. 10,225,858 issued on Mar. 5, 2019), which claims thepriority benefit under 35 U.S.C. § 119(e) to U.S. ProvisionalApplication No. 62/106,733 filed on Jan. 23, 2015, all of which arehereby expressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method for selecting of sidelink grant for a D2DUE in a D2D (Device to Device) communication system and a devicetherefor.

Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARM)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, the standardinstitute such as 3GPP or IEEE has proceeded to establish the D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that the D2D communication contributes to increasethroughput of a mobile communication system and create new communicationservices. Also, the D2D communication may support proximity based socialnetwork services or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

The D2D communication technologies such as infrared communication,ZigBee, radio frequency identification (RFID) and near fieldcommunications (NFC) based on the RFID have been already used. However,since these technologies support communication only of a specific objectwithin a limited distance (about 1 m), it is difficult for thetechnologies to be regarded as the D2D communication technologiesstrictly.

Although the D2D communication has been described as above, details of amethod for transmitting data from a plurality of D2D user equipmentswith the same resource have not been suggested.

SUMMARY OF THE INVENTION

The object of the present invention can be achieved by providing amethod for operating by an apparatus in wireless communication system,the method comprising; configuring a resource pool in which the UEselects a sidelink grant for transmitting sidelink data; and selecting afirst set of sidelink grants for a first Sidelink Control period (SCperiod) from the resource pool to transmit a sidelink data; andselecting a second set of sidelink grants for a second SC period fromthe resource pool if amount of available sidelink data cannot betransmitted using remaining sidelink grants among the first set ofsidelink grants in the first SC period, wherein the remaining sidelinkgrants among the first set of sidelink grants are sidelink grantsconfigured in one or more subframes within the first SC period startingfrom a subframe in which the UE selects the second sidelink grant to alast subframe of the first SC period.

In another aspect of the present invention provided herein is an UEoperating in wireless communication system, the UE comprising: a RFmodule; and processor configured to control the RF module, wherein theprocessor is configured to configure a resource pool in which the UEselects a sidelink grant for transmitting sidelink data, to select afirst set of sidelink grants for a first Sidelink Control period (SCperiod) from the resource pool to transmit a sidelink data, and toselect a second set of sidelink grants for a second SC period from theresource pool if amount of available sidelink data cannot be transmittedusing remaining sidelink grants among the first set of sidelink grantsin the first SC period, wherein the remaining sidelink grants among thefirst set of sidelink grants are sidelink grants configured in one ormore subframes within the first SC period starting from a subframe inwhich the UE selects the second sidelink grant to a last subframe of thefirst SC period.

Preferably, the second set of sidelink grants is selected fortransmitting available sidelink data except sidelink data that can betransmitted using remaining sidelink grants in the first SC period.

Preferably, if amount of available sidelink data can be transmittedusing remaining sidelink grants among the first set of sidelink grantsin the first SC period, the sidelink data is transmitted in the first SCperiod using the remaining sidelink grants among the first set ofsidelink grant.

Preferably, if amount of available sidelink data can be transmittedusing remaining sidelink grants among the first set of sidelink grantsin the first SC period, the UE does not select the second set ofsidelink grants from the resource pool

Preferably, when the UE selects the second set of sidelink grants fromthe resource pool, the UE considers that the second set of sidelinkgrants is associated with a second SC period which starts at least 4subframes after a subframe in which the UE selects the second set ofsidelink grants.

In another aspect of the present invention, provided herein is a methodfor a UE (User Equipment) operating in a wireless communication system,the method comprising: configuring a resource pool in which the UEselects a sidelink grant for Sidelink Control Information (SCI) andSidelink Traffic Channel (STCH) transmission; and selecting a sidelinkgrant from the resource pool if more data is available in a STCH thancan be transmitted in a current Sidelink Control period (SC period).

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture;

FIG. 10 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 11A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 11B is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery;

FIG. 13 is a diagram for a general overview of the LTE protocolarchitecture for the downlink;

FIG. 14 is a diagram for selecting of sidelink grant for a D2D UE in aD2D communication system according to embodiments of the presentinvention; and

FIG. 15A and 15B are examples for selecting of sidelink grant for a D2DUE in a D2D communication system according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprise a DSP/microprocessor(110) and RF module (transceiver; 135). The DSP/microprocessor (110) iselectrically connected with the transceiver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. The receiver and the transmitter canconstitute the transceiver (135). The UE further comprises a processor(110) connected to the transceiver (135: receiver and transmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals)

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture.

PC1 to PC 5 represent interfaces. PC1 is a reference point between aProSe application in a UE and a ProSe App server. It is used to defineapplication level signaling requirements. PC 2 is a reference pointbetween the ProSe App Server and the ProSe Function. It is used todefine the interaction between ProSe App Server and ProSe functionalityprovided by the 3GPP EPS via ProSe Function. One example may be forapplication data updates for a ProSe database in the ProSe Function.Another example may be data for use by ProSe App Server in interworkingbetween 3GPP functionality and application data, e.g. name translation.PC3 is a reference point between the UE and ProSe Function. It is usedto define the interaction between UE and ProSe Function. An example maybe to use for configuration for ProSe discovery and communication. PC4is a reference point between the EPC and ProSe Function. It is used todefine the interaction between EPC and ProSe Function. Possible usecases may be when setting up a one-to-one communication path between UEsor when validating ProSe services (authorization) for session managementor mobility management in real time.

PC5 is a reference point between UE to UE used for control and userplane for discovery and communication, for relay and one-to-onecommunication (between UEs directly and between UEs over LTE-Uu).Lastly, PC6 is a reference point may be used for functions such as ProSeDiscovery between users subscribed to different PLMNs.

EPC (Evolved Packet Core) includes entities such as MME, S-GW, P-GW,PCRF, HSS etc. The EPC here represents the E-UTRAN Core Networkarchitecture. Interfaces inside the EPC may also be impacted albeit theyare not explicitly shown in FIG. 9.

Application servers, which are users of the ProSe capability forbuilding the application functionality, e.g. in the Public Safety casesthey can be specific agencies (PSAP) or in the commercial cases socialmedia. These applications are defined outside the 3GPP architecture butthere may be reference points towards 3GPP entities. The Applicationserver can communicate towards an application in the UE.

Applications in the UE use the ProSe capability for building theapplication functionality. Example may be for communication betweenmembers of Public Safety groups or for social media application thatrequests to find buddies in proximity. The ProSe Function in the network(as part of EPS) defined by 3GPP has a reference point towards the ProSeApp Server, towards the EPC and the UE.

The functionality may include but not restricted to e.g.:

Interworking via a reference point towards the 3rd party Applications;

Authorization and configuration of the UE for discovery and Directcommunication;

Enable the functionality of the EPC level ProSe discovery;

ProSe related new subscriber data and/handling of data storage; alsohandling of ProSe identities;

Security related functionality;

Provide Control towards the EPC for policy related functionality;

Provide functionality for charging (via or outside of EPC, e.g. offlinecharging);

Especially, the following identities are used for ProSe DirectCommunication:

Source Layer-2 ID identifies a sender of a D2D packet at PC5 interface.The Source Layer-2 ID is used for identification of the receiver RLC UMentity;

Destination Layer-2 ID identifies a target of the D2D packet at PC5interface. The Destination Layer-2 ID is used for filtering of packetsat the MAC layer. The Destination Layer-2 ID may be a broadcast,groupcast or unicast identifier; and

SA L1 ID identifier in Scheduling Assignment (SA) at PC5 interface. SAL1 ID is used for filtering of packets at the physical layer. The SA L1ID may be a broadcast, groupcast or unicast identifier.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID and Destination Layer-2 ID in the UE. Thisinformation is provided by higher layers.

In case of groupcast and unicast, the MAC layer will convert the higherlayer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifyingthe target (Group, UE) into two bit strings of which one can beforwarded to the physical layer and used as SA L1 ID whereas the otheris used as Destination Layer-2 ID. For broadcast, L2 indicates to L1that it is a broadcast transmission using a pre-defined SA L1 ID in thesame format as for group- and unicast.

FIG. 10 is a conceptual diagram illustrating for a Layer 2 structure forSidelink.

The Sidelink is UE to UE interface for ProSe direct communication andProSe Direct Discovery. Corresponds to the PC5 interface. The Sidelinkcomprises ProSe Direct Discovery and ProSe Direct Communication betweenUEs. The Sidelink uses uplink resources and physical channel structuresimilar to uplink transmissions. However, some changes, noted below, aremade to the physical channels. E-UTRA defines two MAC entities; one inthe UE and one in the E-UTRAN. These MAC entities handle the followingtransport channels additionally, i) sidelink broadcast channel (SL-BCH),ii) sidelink discovery channel (SL-DCH) and iii) sidelink shared channel(SL-SCH).

Basic transmission scheme: the Sidelink transmission uses the same basictransmission scheme as the UL transmission scheme. However, sidelink islimited to single cluster transmissions for all the sidelink physicalchannels. Further, sidelink uses a 1 symbol gap at the end of eachsidelink sub-frame.

Physical-layer processing: the Sidelink physical layer processing oftransport channels differs from UL transmission in the following steps:

i) Scrambling: for PSDCH and PSCCH, the scrambling is not UE-specific;

ii) Modulation: 64 QAM is not supported for Sidelink.

Physical Sidelink control channel: PSCCH is mapped to the Sidelinkcontrol resources. PSCCH indicates resource and other transmissionparameters used by a UE for PSSCH.

Sidelink reference signals: for PSDCH, PSCCH and PSSCH demodulation,reference signals similar to uplink demodulation reference signals aretransmitted in the 4th symbol of the slot in normal CP and in the 3rdsymbol of the slot in extended cyclic prefix. The Sidelink demodulationreference signals sequence length equals the size (number ofsub-carriers) of the assigned resource. For PSDCH and PSCCH, referencesignals are created based on a fixed base sequence, cyclic shift andorthogonal cover code.

Physical channel procedure: for in-coverage operation, the powerspectral density of the sidelink transmissions can be influenced by theeNB.

FIG. 11A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 11b is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 11A shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 11A.

User plane details of ProSe Direct Communication: i) There is no HARQfeedback for ProSe Direct Communication, ii) RLC UM is used for ProSeDirect Communication, iii) A receiving UE needs to maintain at least oneRLC UM entity per transmitting peer UE; iv) A receiving ProSe-RLC UMentity used for ProSe Direct Communication does not need to beconfigured prior to reception of the first RLC UMD PDU; v) ROHCUnidirectional-Mode is used for header compression in PDCP for ProSeDirect Communication.

A UE may establish multiple logical channels. LCID included within theMAC subheader uniquely identifies a logical channel within the scope ofone Source Layer-2 ID and ProSe Layer-2 Group ID combination. Parametersfor logical channel prioritization are not configured.

FIG. 11B shows the protocol stack for the control plane.

A UE does not establish and maintain a logical connection to receivingUEs prior to a ProSe Direct Communication.

In order to perform synchronization UE(s) may transmit synchronizationsignal and SBCCH and become synchronization source. The Access Stratumprotocol stack for SBCCH in the PC5 interface consists of RRC, RLC, MACand PHY as shown FIG. 11B.

The UE supporting ProSe Direct Communication can operate in two modesfor resource allocation:

Mode 1 is a Scheduled resource allocation. In this case, the UE needs tobe RRC_CONNECTED in order to transmit data. The UE requests transmissionresources from the eNB. The eNB schedules transmission resources fortransmission of Sidelink Control and data. The UE sends a schedulingrequest (D-SR or Random Access) to the eNB followed by a ProSe BSR.Based on the ProSe BSR the eNB can determine that the UE has data for aProSe Direct Communication transmission and estimate the resourcesneeded for transmission. eNB can schedule transmission resources forProSe Direct Communication using configured SL-RNTI.

Mode 2 is an autonomous resource selection. In this case, a UE on itsown selects resources from resource pools to transmit Sidelink Controland data. A UE in RRC_CONNECTED may send the ProSe Direct indication toeNB when UE becomes interested in ProSe Direct Communication. Inresponse eNB may configure the UE with a SL-RNTI. A UE is consideredin-coverage for ProSe Direct Communication whenever it detects a cell ona Public Safety ProSe Carrier as per criteria.

The resource pools for Sidelink Control when the UE is out of coverageare configured as below: i) the resource pool used for reception ispre-configured; or ii) the resource pool used for transmission ispre-configured.

The resource pools for Sidelink Control when the UE is in coverage areconfigured as below: i) the resource pool used for reception isconfigured by the eNB via RRC, in broadcast signaling; or ii) theresource pool used for transmission is configured by the eNB via RRC, indedicated or broadcast signaling, if UE autonomous resource selection isused; or iii) the resource pool used for transmission is configured bythe eNB via RRC, in dedicated signaling if scheduled resource allocationis used. The eNB schedules the specific resource(s) for Sidelink Controltransmission within the configured reception pool.

The resource pools for data when the UE is out of coverage areconfigured as below: i) the resource pool used for reception ispre-configured; and ii) the resource pool used for transmission ispre-configured.

The resource pools for data when the UE is in coverage are configured asbelow: i) the resource pools used for transmission and reception areconfigured by the eNB via RRC, in dedicated or broadcast signaling, ifUE autonomous resource selection is used; ii) there is no resource poolfor transmission if scheduled resource allocation is used.

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery.

ProSe Direct Discovery is defined as the procedure used by the UEsupporting Direct Discovery to discover other UE(s) in its proximity,using E-UTRA direct radio signals via PC5. ProSe Direct Discovery issupported only when the UE is served by E-UTRAN.

The UE can participate in announcing and monitoring of discovery messagein both RRC_IDLE and RRC_CONNECTED states as per eNB configuration. TheUE announces and monitors its discovery message subject to thehalf-duplex constraint.

The UE that participates in announcing and monitoring of discoverymessages maintains the current UTC time. The UE that participates inannouncing transmits the discovery message which is generated by theProSe Protocol taking into account the UTC time upon transmission of thediscovery message. In the monitoring UE the ProSe Protocol provides themessage to be verified together with the UTC time upon reception of themessage to the ProSe Function.

Radio Protocol Stack (AS) for ProSe Direct Discovery consists of onlyMAC and PHY.

The AS layer performs the following functions: i) Interfaces with upperlayer (ProSe Protocol): The MAC layer receives the discovery messagefrom the upper layer (ProSe Protocol). The IP layer is not used fortransmitting the discovery message, ii) Scheduling: The MAC layerdetermines the radio resource to be used for announcing the discoverymessage received from upper layer, iii) Discovery PDU generation: TheMAC layer builds the MAC PDU carrying the discovery message and sendsthe MAC PDU to the physical layer for transmission in the determinedradio resource. No MAC header is added.

In case of UE autonomous resource selection, the eNB provides the UE(s)with the resource pool configuration used for announcing of discoverymessage. The configuration may be signaled in broadcast or dedicatedsignaling. The UE autonomously selects radio resource(s) from theindicated resource pool and announces discovery message, and the UE canannounce discovery message on a randomly selected discovery resourceduring each discovery period.

Meanwhile, in case of Scheduled resource allocation, the UE inRRC_CONNECTED may request resource(s) for announcing of discoverymessage from the eNB via RRC. The eNB assigns resource(s) via RRC, andthe resources are allocated within the resource pool that is configuredin UEs for monitoring.

For UEs in RRC_IDLE, the eNB may select one of the following options: i)The eNB may provide a resource pool for UE autonomous resource selectionbased discovery message announcement in SIB 19. UEs that are authorizedfor Prose Direct Discovery use these resources for announcing discoverymessage in RRC_IDLE, ii) The eNB may indicate in SIB 19 that it supportsProSe Direct Discovery but does not provide resources for discoverymessage announcement. UEs need to enter RRC_CONNECTED in order torequest resources for discovery message announcement.

For UEs in RRC_CONNECTED, A UE authorized to perform ProSe DirectDiscovery announcement indicates to the eNB that it wants to performProSe Direct Discovery announcement. The eNB validates whether the UE isauthorized for ProSe Direct Discovery announcement using the UE contextreceived from MME. The eNB may configure the UE with resource pool forUE autonomous resource selection for discovery message announcement viadedicated signaling. The eNB may configure resource pool along withdedicated resource in the form of time and frequency indices fordiscovery message announcement via dedicated RRC signaling. Thededicated resources allocated by the eNB are valid until the eNBre-configures the resource(s) by RRC signaling or, the UE entersRRC_IDLE.

Authorized receiving UEs in RRC_IDLE and RRC_CONNECTED monitor resourcepools used for UE autonomous resource selection and resource pools forscheduled resource allocation. The eNB provides the resource poolconfiguration used for discovery message monitoring in SIB 19. The SIB19 may contain detailed ProSe Direct Discovery configuration used forannouncing in neighbor cells of intra-frequency as well.

Synchronous and asynchronous deployments are supported. Discoveryresources can be overlapping or non-overlapping across cells.

A UE if authorized by the NW can announce discovery message only onserving cell. The UE can monitor discovery resources in the same as wellas other frequencies than the serving cell, in same or different PLMNs.

FIG. 13 is a diagram for a general overview of the LTE protocolarchitecture for the downlink.

A general overview of the LTE protocol architecture for the downlink isillustrated in FIG. 13. Furthermore, the LTE protocol structure relatedto uplink transmissions is similar to the downlink structure in FIG. 13,although there are differences with respect to transport formatselection and multi-antenna transmission.

Data to be transmitted in the downlink enters in the form of IP packetson one of the SAE bearers (1301). Prior to transmission over the radiointerface, incoming IP packets are passed through multiple protocolentities, summarized below and described in more detail in the followingsections:

Packet Data Convergence Protocol (PDCP, 1303) performs IP headercompression to reduce the number of bits necessary to transmit over theradio interface. The header-compression mechanism is based on ROHC, astandardized header-compression algorithm used in WCDMA as well asseveral other mobile-communication standards. PDCP (1303) is alsoresponsible for ciphering and integrity protection of the transmitteddata. At the receiver side, the PDCP protocol performs the correspondingdeciphering and decompression operations. There is one PDCP entity perradio bearer configured for a mobile terminal.

Radio Link Control (RLC, 1305) is responsible forsegmentation/concatenation, retransmission handling, and in-sequencedelivery to higher layers. Unlike WCDMA, the RLC protocol is located inthe eNodeB since there is only a single type of node in the LTEradio-access-network architecture. The RLC (1305) offers services to thePDCP (1303) in the form of radio bearers. There is one RLC entity perradio bearer configured for a terminal.

There is one RLC entity per logical channel configured for a terminal,where each RLC entity is responsible for: i) segmentation,concatenation, and reassembly of RLC SDUs; ii) RLC retransmission; andiii) in-sequence delivery and duplicate detection for the correspondinglogical channel.

Other noteworthy features of the RLC are: (1) the handling of varyingPDU sizes; and (2) the possibility for close interaction between thehybrid-ARQ and RLC protocols. Finally, the fact that there is one RLCentity per logical channel and one hybrid-ARQ entity per componentcarrier implies that one RLC entity may interact with multiplehybrid-ARQ entities in the case of carrier aggregation.

The purpose of the segmentation and concatenation mechanism is togenerate RLC PDUs of appropriate size from the incoming RLC SDUs. Onepossibility would be to define a fixed PDU size, a size that wouldresult in a compromise. If the size were too large, it would not bepossible to support the lowest data rates. Also, excessive padding wouldbe required in some scenarios. A single small PDU size, however, wouldresult in a high overhead from the header included with each PDU. Toavoid these drawbacks, which is especially important given the verylarge dynamic range of data rates supported by LTE, the RLC PDU sizevaries dynamically.

In process of segmentation and concatenation of RLC SDUs into RLC PDUs,a header includes, among other fields, a sequence number, which is usedby the reordering and retransmission mechanisms. The reassembly functionat the receiver side performs the reverse operation to reassemble theSDUs from the received PDUs.

Medium Access Control (MAC, 1307) handles hybrid-ARQ retransmissions anduplink and downlink scheduling. The scheduling functionality is locatedin the eNodeB, which has one MAC entity per cell, for both uplink anddownlink. The hybrid-ARQ protocol part is present in both thetransmitting and receiving end of the MAC protocol. The MAC (1307)offers services to the RLC (1305) in the form of logical channels(1309).

Physical Layer (PHY, 1311), handles coding/decoding,modulation/demodulation, multi-antenna mapping, and other typicalphysical layer functions. The physical layer (1311) offers services tothe MAC layer (1307) in the form of transport channels (1313).

The physical layer offers information transfer services to MAC andhigher layers. The physical layer transport services are described byhow and with what characteristics data are transferred over the radiointerface. An adequate term for this is “Transport Channel”.

Downlink transport channel types are:

1. Broadcast Channel (BCH) characterized by, i) fixed, pre-definedtransport format, ii) requirement to be broadcast in the entire coveragearea of the cell.

2. Downlink Shared Channel (DL-SCH) characterized by, i) support forHARQ, ii) support for dynamic link adaptation by varying the modulation,coding and transmit power, iii) possibility to be broadcast in theentire cell, iv) possibility to use beamforming, v) support for bothdynamic and semi-static resource allocation, vi) support for UEdiscontinuous reception (DRX) to enable UE power saving.

3. Paging Channel (PCH) characterized by, i) support for UEdiscontinuous reception (DRX) to enable UE power saving (DRX cycle isindicated by the network to the UE), ii) requirement to be broadcast inthe entire coverage area of the cell, iii) mapped to physical resourceswhich can be used dynamically also for traffic/other control channels.

4. Multicast Channel (MCH) characterized by, i) requirement to bebroadcast in the entire coverage area of the cell, ii) support for MBSFNcombining of MBMS transmission on multiple cells, iii) support forsemi-static resource allocation e.g. with a time frame of a long cyclicprefix.

Uplink transport channel types are:

1. Uplink Shared Channel (UL-SCH) characterized by, i) possibility touse beamforming, ii) support for dynamic link adaptation by varying thetransmit power and potentially modulation and coding, iii) support forHARQ, iv) support for both dynamic and semi-static resource allocation.

2. Random Access Channel(s) (RACH) characterized by, i) limited controlinformation, ii) collision risk.

Sidelink transport channel types are:

1. Sidelink broadcast channel (SL-BCH) characterized by pre-definedtransport format.

2. Sidelink discovery channel (SL-DCH) characterized by, i) fixed size,pre-defined format periodic broadcast transmission, ii) support for bothUE autonomous resource selection and scheduled resource allocation byeNB, iii) collision risk due to support of UE autonomous resourceselection; no collision when UE is allocated dedicated resources by theeNB.

3. Sidelink shared channel (SL-SCH) characterized by, i) support forbroadcast transmission, ii) support for both UE autonomous resourceselection and scheduled resource allocation by eNB, iii) collision riskdue to support of UE autonomous resource selection; no collision when UEis allocated dedicated resources by the eNB, iv) support for HARQcombining, but no support for HARQ feedback, v) support for dynamic linkadaptation by varying the transmit power, modulation and coding.

SL-SCH Data Transmission

In order to transmit on the SL-SCH the UE must have a sidelink grant.The sidelink grant is selected as follows:

i) If the UE receives a sidelink grant dynamically on the PDCCH orEPDCCH, the UE shall use the received sidelink grant determine the setof subframes in which transmission of sidelink control information andtransmission of first transport block occur, consider the receivedsidelink grant to be a configured sidelink grant occurring in thosesubframes starting at the beginning of the first available SC Periodwhich starts at least 4 subframes after the subframe in which thesidelink grant was received, overwriting a previously configuredsidelink grant occurring in the same SC period, if available, and clearthe configured sidelink grant at the end of the corresponding SC Period.

ii) If the UE is configured by upper layers to transmit using a pool ofresources as indicated and data is available in STCH and if the UE doesnot have a configured sidelink grant, the UE shall randomly select asidelink grant from the resource pool configured by upper layers. Therandom function shall be such that each of the allowed selections can bechosen with equal probability, use the selected sidelink grant determinethe set of subframes in which transmission of sidelink controlinformation and transmission of first transport block occur, considerthe received sidelink grant to be a configured sidelink grant occurringin those subframes starting at the beginning of the first available SCPeriod which starts at least 4 subframes after the subframe in which thesidelink grant was received, and clear the configured sidelink grant atthe end of the corresponding SC Period.

If the UE has a configured sidelink grant occurring in this subframe,for each subframe, the UE shall instruct the physical layer to transmita scheduling assignment corresponding to the configured sidelink grantif the configured sidelink grant corresponds to transmission of sidelinkcontrol information. Else if the configured sidelink grant correspondsto transmission of first transport block, the UE shall deliver theconfigured sidelink grant and the associated HARQ information to theSidelink HARQ Entity for this subframe.

SL-SCH Data Reception

Scheduling assignments transmitted on the PSCCH indicate if there is atransmission on SL-SCH and provide the relevant HARQ information.

For each subframe during which the UE monitors PSCCH, the UE shall storethe scheduling assignment and associated HARQ information as schedulingassignment valid for the subframes corresponding to first transmissionof each transport block if a scheduling assignment for this subframe hasbeen received on the PSCCH for a Sidelink Scheduling Assignment Identityof interest to this UE.

For each subframe for which the UE has a valid scheduling assignment,the UE shall deliver the scheduling assignment and the associated HARQinformation to the Sidelink HARQ Entity.

In D2D, for a UE in mode 2 operation, the data transmission can besummarized as follows: i) if there is data in STCH and the UE does nothave a configured sidelink grant for the next SC period, the UE selectsan SL grant, ii) Using the selected SL grant, the UE determines thesubframes to transmit SCT and the first TB, iii) The UE considers theselected SL grant as configured SL grant.

Since the SCI includes the information of data transmission, inprinciple, the SCI does not need to be transmitted in case there is nodata to transmit. Once the transmitting UE in mode 2 selects the SLgrant, the UE will transmit SCI to the receiving UE. From the receivingUE point of view, if the receiving UE receives a SCI, the UE willunnecessarily perform the HARQ process even though there is no receivedTB. Therefore, it is desirable for a UE to select the SL grant only incase there is data available for transmission in the SC period withwhich the SL grant is associated.

FIG. 14 is a diagram for selecting of sidelink grant for a D2D UE in aD2D communication system according to embodiments of the presentinvention.

In this invention, in order to select an SL grant, when the UE checkswhether there is data available in STCH, the UE considers only the datato be transmitted in the next SC period associated with the SL grant.For this, when the UE checks whether there is data available in STCH,the UE shall not consider the data which can be transmitted in thecurrent on-going SC period.

The UE configures a resource pool in which the UE selects a sidelinkgrant for transmitting sidelink data (S1401), and selects a first set ofsidelink grants for a current SC period from the resource pool totransmit a sidelink data (S1403).

The eNB configures a UE to select an SL grant by UE itself and, the eNBconfigures a resource pool for a UE in which the UE selects an SL grantfor SCI and STCH data transmission.

If the UE is configured to select a second SL grant by UE itself, the UEchecks whether amount of available sidelink data cannot be transmittedusing remaining sidelink grants among the first set of sidelink grantsin the current SC period (S1405).

It means that the UE checks whether data is available in STCH asfollows: i) the data which is in STCH and to be transmitted in thecurrent on-going SC period shall not be considered as ‘the dataavailable in STCH’, ii) the data which is in STCH but cannot betransmitted in the current on-going SC period shall be considered as‘the data available in STCH’.

If amount of available sidelink data cannot be transmitted usingremaining sidelink grants among the first set of sidelink grants in thefirst SC period, the UE selects a second set of sidelink grants for anext SC period from the resource pool (S1407).

Preferably, the remaining sidelink grants among the first set ofsidelink grants are sidelink grants configured in one or more subframeswithin the first SC period starting from a subframe in which the UEselects the second sidelink grant to a last subframe of the first SCperiod.

If amount of available sidelink data can be transmitted using remainingsidelink grants among the first set of sidelink grants in the current SCperiod, the sidelink data is transmitted in the current SC period usingthe remaining sidelink grants among the first set of sidelink grantinstead of selecting second set of sidelink grants for a next SC periodfrom the resource pool (S1409).

In other word, if there is ‘data available in STCH’, the UE selects anSL grant in the resource pool and considers that the SL grant isassociated with the second SC period which starts at least 4 subframesafter the subframe in which the UE selects the SL grant, and if there isno ‘data available in STCH’, the UE does not select an SL grant.

FIGS. 15A and 15B are examples for selecting of sidelink grant for a D2DUE in a D2D communication system according to embodiments of the presentinvention.

Regarding FIG. 15A, the UE is configured to select an SL grant by itself(S1501 a). The UE is configured with a resource pool where the UEselects an SL grant (S1503 a). In SC Period #1, there is Data1, Data2,Data 3 in STCH.

The UE can transmit Data 1, Data 2, and Data 3 using the SL grantconfigured for the SC Period #1 (S1505 a).

The UE checks whether there is ‘data available in STCH’ (S1507 a).

Since Data1, Data2, and Data3 can be transmitted in SC Period #1, the UEdoes not select an SL grant for SC period #2 (S1509 a).

Regarding FIG. 15B, the UE is configured to select an SL grant by itself(S1501 b). The UE is configured with a resource pool where the UEselects an SL grant (S1503 b). In SC Period #1, there is Data1, Data2,Data 3 in STCH.

The UE can transmit Data 1 and Data 2 using the SL grant configured forthe SC Period #1, but the UE cannot transmit Data 3 using the SL grantconfigured for the SC period #1 (S1505 b).

The UE checks whether there is ‘data available in STCH’ (S1507 b).

Since Data3 cannot be transmitted in SC Period #1, the UE considers thatthere is ‘data available in STCH’ and selects an SL grant for SC period#2 (S1509 b).

In conclusion, if the MAC entity is configured by upper layers totransmit using a pool of resources and more data is available in STCHthan can be transmitted in the current SC period (or more data isavailable in STCH except the data which can be transmitted in thecurrent on-going SC Period) and if the MAC entity does not have aconfigured sidelink grant, the MAC entity shall:

i) randomly select a sidelink grant from the resource pool configured byupper layers. The random function shall be such that each of the allowedselections can be chosen with equal probability;

ii) using the selected sidelink grant determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

iii) consider the selected sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was selected;

iv) clear the configured sidelink grant at the end of the correspondingSC Period.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

What is claimed is:
 1. A method for transmitting sidelink data by a UserEquipment (UE) in a wireless communication system, the methodcomprising: determining whether resource pool information for selectinga sidelink grant is configured by a base station; determining whethermore sidelink data is available in a Sidelink Traffic Channel (STCH)than can be transmitted in a current Sidelink Control (SC) period;selecting resources for the sidelink grant from the resource poolinformation based on the resource pool information for selecting thesidelink grant being configured by the base station, and more sidelinkdata being available in the STCH than can be transmitted in the currentSC period; selecting resources for the sidelink data based on theresources for the sidelink grant; and transmitting the sidelink data toanother UE through the resources for the sidelink data, wherein thesidelink grant is for a next SC period after the current SC period. 2.The method according to claim 1, further comprising: determining a setof time intervals using the sidelink grant, wherein the sidelink grantis considered to be a configured sidelink grant occurring in the set oftime intervals starting at a beginning of a first available SC periodwhich starts at least N time intervals after a time interval in whichthe sidelink grant is selected, and wherein N is a positive integer. 3.The method according to claim 1, further comprising: clearing thesidelink grant at an end of the next SC period.
 4. The method accordingto claim 1, wherein the UE is a Device-to-Device UE in Mode
 2. 5. A UserEquipment (UE) transmitting sidelink data in a wireless communicationsystem, the UE comprising: a transceiver; and a processor configured to:determine whether resource pool information for selecting a sidelinkgrant is configured by a base station; determine whether more sidelinkdata is available in a Sidelink Traffic Channel (STCH) than can betransmitted in a current Sidelink Control (SC) period; select resourcesfor the sidelink grant from the resource pool information based on theresource pool information for selecting the sidelink grant beingconfigured by the base station, and more sidelink data being availablein the STCH than can be transmitted in the current SC period; selectresources for the sidelink data based on the resources for the sidelinkgrant; and transmit the sidelink data to another UE through theresources for the sidelink data, wherein the sidelink grant is for anext SC period after the current SC period.
 6. The UE according to claim5, wherein the processor is further configured to: determine a set oftime intervals using the sidelink grant, wherein the sidelink grant isconsidered to be a configured sidelink grant occurring in the set oftime intervals starting at a beginning of a first available SC periodwhich starts at least N time intervals after a time interval in whichthe sidelink grant is selected, and wherein N is a positive integer. 7.The UE according to claim 5, wherein the processor is further configuredto: clear the sidelink grant at an end of the next SC period.
 8. The UEaccording to claim 5, wherein the UE is a Device-to-Device UE in Mode 2.